Computer control system for refining and hydrogenation of unsaturated hydrocarbons

ABSTRACT

Described is a control system for a refining hydrogenation and deodorizing plant for edible oils and the like wherein various system variables are converted into signals which are fed to a computer which controls the system to optimize performance and reduce oil losses.

United StatesPatent 11 1 Putman COMPUTER CONTROL SYSTEM FOR REFINING ANDHYDROGENATION OF UNSATURATED HYDROCARBONS [75] Inventor: Richard E.Putman, Pittsburgh, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[62] Division of Ser. No. 885,405, Dec. 16, 1969, Pat. No. I

[52] US. Cl 23/253 A, 23/260, 23/285,

260/409, 260/690, 260/698, 260/700 [51] Int. Cl. B01j 1/00, CO7c 3/12,GOln 27/00 [58] Field of Search 23/253 A, 230 A, 253 R,

23/260, 285; 260/690, 698, 700, 409; 208/DIG. l; 235/15l.l2 R, 151.12MO,

I 111 3,798,002 1 1 Mar. 19, 1974 FOREIGN PATENTS OR APPLICATIONS239,650 11/1969 U.S.S.R 23/253 A Primary. Examiner-Joseph ScovronekAttorney. Agent, or FirmR. G. Brodahl 57 ABSTRACT Described is a controlsystem for a refining hydrogenation and deodorizing plant-for edibleoils and the like wherein various system variables are converted intosignals which are fed to a computer which con trols the system tooptimize performance and reduce [56] References Cited oil losses.

UNITED STATES PATENTS 3,228,858 1/1966 Matyear 260/683.9 X 4 Claims, 3Drawing Figures FROM COMPUTER |0O\ THERMAL H2 PURGE F CONDUCTIVITY D 3sANALYZER 128 124 94 11a 112' TEMPERATURE PRESSURE 96 CONTROL comm.

in H2 I04 TO COMPUTER Y cousnmr DISPLACEMENT PUMP 1 COMPUTER CONTROLSYSTEM FOR REFINING AND HYDROGENATION OF UNSATURATED HYDROCARBONSCROSS-REFERENCES TO RELATED APPLICATIONS This application is a divisionof application, Ser. No. 885,405, filed Dec. 16, 1969, now US. Pat. No.3,653,842 issued Apr. 4, 1972. 1

BACKGROUND OF THE INVENTION The object of refining is to remove the freefatty acids by neutralizing with a caustic, usually sodium hydroxide,and to remove the phosphatides, proteins or other substances which,after hydration, report to the soap stock in passing through acentrifuge or separator. The oil is pumped with a proportional amount ofcaustic of 2 predetermined concentration to mixers in which much of thechemical reaction takes place. The reactions include neutralization ofthe free fatty-acids and hydration of gums and the like. The resultingmaterial then passes through a heat exchanger where the tempera- 30 tureis raised to approximately 150F, and then to primary separators in whichthe gums and soaps are separated from the neutral oil. The neutral oil,containing traces of sodium and water, then passes through a second heatexchanger to a mixer, into which is also fed 3 heated water togetherwith a small amount of phosphoric acid for the neutralization of anycaustic carried over with the neutral oil. This mixed liquid is thenpumped to secondary or washing separators. Here the neutral oil isseparated from the water and is pumped 40 to a vacuum drier in which anywater .remaining in the oil is removed.

After Winterizing to remove glycerides, the oil is pumped from storageand passes through a heat ex changer where it is heated to approximately250F be 4 fore entering the hydrogenation converter. A catalyst of asuitable grade is slurrified with the oil and pumped into the converter.Hydrogen is then bubbled through the heated oil, in which process theunsaturated oilis converted toahydrogenated or saturated oil which willharden upon cooling. .Finally, the oilis processed in a deodorizingvacuum chamber where volatiles are removed and the remaining free fattyacids are recovered. 5

ln the refining process, enough caustic should be added to remove thefree fatty acids and other impurities. However, if too much caustic is.added,.it converts the desired oil into a soap which is lost in acentrifuge. In the past, the efficiency of the refining process in termsof oil loss has been determined only at the end of a processing cyclefora batch of oil. In other words,

excessive caustic addition and soap generation was determined after thefact" when it was too late to correct the matter for a particular batch.

ln a somewhat similar manner, the degree of hydrogenation has heretoforebeen determined after the fact by taking a sample of the oil anddetermining the iodine value which is linearly related to the amount ofhydrogen absorbed by the oil. No known satisfactory means has beendevised for continually monitoring the amountof hydrogen absorption todetermine the end point of the hydrogenation process.

SUMMARY OF THE INVENTION As an overall object, the present inventionseeks to provide a computer control system for an oil refining andhydrogenation plant whereby the process can be Another object of theinvention is to provide a method for controlling hydrogenation ofunsaturated hydrocarbons by a comparison of the mass flow rates ofhydrogen into and out of a bath of oil to be hydrogenated. Still anotherobject of the invention is to provide a new'and improved system fordeodorizing edible hydrogenated oil by elimination of volatilematerials.

In accordance with the invention, optimization of the refining processis achieved by causing a computer; to periodically make a deliberatechange in the caustic-tooil flow ratio. The computer also measures thecorresponding change in sodium content of the neutral oil, without atthis time making a correcting adjustment to back pressure at the outputof a centrifuge. If the sodium is deficient, only a small change insodium in the neutral oil will be detected since the sodium will reactwith the free fatty acids. If the sodium is in excess, a small changewill again be recorded due to saponifcation. The largest change willoccur with-maximum neutralization of free fatty acids at minimumsaponification of neutral oil. Thus, the computer, by making a series ofsmall changes in the caustic-to-crude oil ratio first in one direction,then in the other and noting the effect on sodium in neutral oil,adjusting back pressure and repeating the process, can establish theoptimum caustic-to-crude oil ratio for a given crude. By controlling thesodium content in the neutral-oil at an agreed low level, the neutraloil recovery rate also will beopti- 'mized.

In the hydrogenation process, hydrogen is bubbled through heatedunsaturated oil, most of the gas passing through the oil being pumpedback to the inlet. Howas to hold it at some maximum level. Furthermore,

from a consideration of. the amount of hydrogen fed into the system andthat purged; with the nitrogen, the total hydrogen absorbed can bedetermined to deter-. mine the end point of the hydrogenation process.

In the deodorizing of the refined oil, the oil is placed within acontainer and a vacuum is created above the I oil by means of steamejectors. Completion of the deodorizing process is determined by meansof a total hydrocarbons analyzer which determines the rate of change ofvolatile content in the. vapor.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in which:

FIG. l is a schematic diagram of the crude oil refining system forunsaturated oils showing the manner in which it is controlled by meansof a computer in accordance with the invention;

FIG. 2 is a schematic diagram of hydrogenation apparatus for unsaturatedoils showing the manner in which it is controlled by means of a computerin accordance with the invention; and

FIG. 3 is a schematic diagram of an oil deodorizing system showing'themanner in which it is controlled by means ofa computer in accordancewith the invention.

a means of pump 18 to a first positive displacement flowmeter 20 andthence to a density meter 22 which may be of the weighted U-tube type.The signals from flowmeter 20 and density meter 22 are fed to thecomputer 10 as shown.

separated from the water and is thereafter pumped to a vacuum drier 58where any water remaining in the oil is removed. The refined oil is thenpumped by pump 601 to a refined oil tank 62 where it is storedpreparatory After passing through the density meter 22, the crude oilpasses through a three-way valve 24, after which water from storage tank25 and a caustic such as sodium hydroxide from a caustic feed tank 27 isadded to the oil via conduits 26' and 28.The mixture then passes to amixer 30 where much of the chemical reaction between the caustic andfree fatty acids as well as hydration occurs. The mixture then passesthrough a heat exchanger 32 where the temperature is raised toapproximately l50F and then to a first centrifuge 34. The centrifuge 34,which operates on the principle of differential specific gravities,causes the mixture to rotate whereby the heavier soaps and impuritieswill be caused to flow radially outwardly while the refined oilConnected to the conduit carrying the refined oil intermediate theflowmeter and density meter 42 is a flame photometer 44 designed for themeasurement of sodium concentration. The photometer 44, therefore,provides a means for determining whether excess sodium has been added tothe oil. The analyzer 44 also produces an electrical signal which is fedto the input of computer 10.

After passing through density meter 42, the oil passes through a thirdthree-way valve 46 and thence through a heat exchanger 48 to a mixingtank 50 where it is mixed with water and phosphoric acid supplied from astorage tank 52. The phosphoric acid, which is added to its beinghydrogenated.

The lye added to the oil from tank 27 consists of sodium hydroxidedissolved in water, the amount of water present varying with sodiumhydroxideconcentration. The caustic-to-oil flow ratio is a chemicalrelationship determined by the need to neutralize the free fatty acidswithout excessive saponification of neutral oil. The water, on the otherhand, all reports to the soap since only traces are found in the neutraloil. The total amount of water added may, therefore, be regarded as thatrequired to insure afree flowing soap.

In the system shown in FIG. 1, the water and lye flow rates arecontrolled separately;.and it is necessary to make up a lye with aconcentration which requires dilution bythe on-line addition of water.This means the system must run with a lye concentration slightly higherthan would ordinarily be thecase.,The water, in passing from tank 25,passes a thermometer 64 and then passes through a flowmeter 66 and avalve 68. An electrical signal proportional to the temperature ofthewater is applied to the computer 10, as is the flow rate asdetermined by the flowmeter 66. The flowmeter 66 also controls acontroller 70 for the valve 68, the set point for the controller beingderived from the output of the computer 10.

Likewise, the caustic solution, as it passes from tank 27, first has itstemperature measured by thermometer 72 and then passes through flowmeter74 and valve 76 before it reaches the mixer 30. Signals proportional totemperature and flow rate from elements 72 and 74 are applied to theinput of the computer 10, the outputof the flowmeter 74 also being usedto control a controller 78 for the valve 76. The controller 78, likecontroller 70, receives the set point signal from the output of thecomputer 10.

Connected to the input and output of the centrifuge 34 are pressuresensing devices 80 and 82. These pressure sensing devices 80 and 82produce electrical signals, proportional to pressure, which are fed backto the input of computer 10. The pressure sensor 82 also serves tocontrol a controller 86 for valve 36, the controller 86 receiving a setpoint signal from the output of computer l0.

.It can be seen, therefore, that the computer controls 7 to the oilwithout excessive saponification of the oil due follows:

G, neutral oil flow as determined by flowmeter 40;

meter 42;

G crude oil flow as determined by flowmeter D crude oil density asdetermined by density meter 22; and

N, neutral oil in crude oil as determined by analysis.

The precision with which this calculation can be carried out dependsupon the accuracy of instrument calibration. lf, during a calibrationrun, the same oil under the same conditions is passed through the twosets of flow and density meters (20, 22 and 40, 42) in series, acalibration factor (fa) can be calculated for the ratio G lG and anothercalibration factor (id) for the ratio D,,/D,. Equation (1) then bcomes:

neutral oil density as determined by density returned to the positionsshown in HO. 1 and the refinwhere:

G, the flow rate as determined by meter 74, and D, K(T, Na where K is aconstant, T is the temperature measured by thermometer 72 and Na is thesodium in the lye as NaOH. 1 Na will be inserted into the computer viaan operators console after laboratory titration of a sample. Thus, bymeasuring temperature via thermometer 72, flow rate via meter 74, andfrom a knowledge of'sodium in the lye. the computer 10 can solveequation (3) above-to determine the flow rate of lye into the mixer 30.This is applied as a set point signal to the controller 78.

Similarly, the computer can compute the amount of.

water. W added with the lye from:

W F, (I00 Na,-/l00) and the amount of dilution water, W added from tank25 from:

where:

6,, water flow rate determined by meter 66;

K a constant; and I T the temperature of the water as determined bythermometer 64.

Thepressure transducers 80 and 82 also send signals to the computer 10indicative of the input and back pressures of the centrifuge 34. If theback pressure should increase without a corresponding increase in inputpressure, it is known that more material is reporting as soap stock.

Optimizing of the process is carried out as follows: the computer canperiodically make a deliberate change (increase) in caustie-to-oil flowratio by adjustment of valve 76 and/or valve 68 and measure thecorresponding change in sodium content by the sodium analyzer 44 withoutat this time making a correcting adjustment to back pressure via valve36. As a diagnostic statement, it can be said that if the sodium isdeficient, only a small change in sodium in the neutral oil will bedetected since the sodium will react with the free fatty acids. If thesodium is in excess, on the other hand, asmall change will again berecorded due to saponification. The largest change'will occur withmaximum neutralization of free fatty acids andminimum sa ponification ofthe neutral oil. Thus, the computer, by making a series of smallvchanges in caustic crude oil ratio first in one direction, then in theother, and noting the effects in the sodium neutral oil, adjusting backpressure via valve 36 and repeating the process, can establish theoptimum sodium hydroxide-crude oil ratio for a given crude. All of this,of course, is controlled primarily by the reading of the sodium analyzer44; while sodium content is varied by. controlling centrifuge backpressure via a set point signal to controller 86. As back pressureincreases, the sodium content will decrease and vice versa, I i

With reference now to FIG. 2, the hydrogenation equipment for the crudeoil refined in the process of FIG. 1 is shown. It includes a reactiontank 94 into which a batch of refined oil is poured up to the level 96.

At the bottom of tank 94 is a conduit 98 having a plurality of openingstherein which permit hydrogen to bubble up through the oil'within thetank. The space above the level 96 in the tank 94 is connected throughconduit 100 and constant displacement pump 102 to the conduit 98. Theconduit 98 is also. connected through control valve 104, a density meter.106 and a flowmeter 108 to a source of hydrogen under pressure. Thesignalsfrom the density meter I06 and flowmeter 108 are applied to thecomputer shown in FIG. 1.. t

The conduit 100 is connected through a second flowmeter 110, a thermalconductivity analyzer 112, a purge valve .1 l4 and a density meter 116to a purge outlet port. The signals from flowmeter 110, thermalconductivity analyzer 112 and density meter 116 areals'o fed back to thecomputer shown in FIG. 1. lnthe space. above the level 96 of the oil intank 94, nitrogen will ac- 'tank 94 is determined by means of-a pressuretransducer 118 which applies a signal back to the computer 10 of FIG. 1.Similarly, the temperature of the oil within tank 94 is measured bythermometer 120 which produces an electrical signal fed back to thecomputer 10. The signal from pressure transducer 118 is utilized by thecomputer to produce a set point signal on lead 122 for a pressurecontroller 124 which regulates the setting of valve 104. The signal fromthermometer 120, when fed back to the computer l0, provides a set pointsignal on lead 126 for a temperature controller 128. The temperaturecontroller 128, in turn, controls a valve I30 supplying cooling water tocooling coilsl 132 within the tank 94.

In the control of the hydrogenation process, the amount of hydrogenflowing into the tank 94 is determined from a consideration of the flowrate and density signals produced by meters l06=and 108. The amount ofhydrogen leaving the system is determined by the thermal conductivityanalyzer in combination with themeters 1 l and 116. The net hydrogenabsorbed by the oil, therefore, is the difference between the amount ofhydrogen flowing into the system and the amount flowing out; and whenthis amount reaches the desired value for a particular weight of oilwithin the tank 94, the process is stopped. The signals from the thermalconductivity analyzer 112 and the meters 110 and 116 also serve toestablish the setting of valve 114, determining the amount of gas whichis purged from the top of the tank 94. As the amount of hydrogen in thepurged gas decreases, it is known that the amount of nitrogen isincreasing and vice versa.

With reference now to FIG 3,*a deodorizer for refined oil is shown. Itincludes a vessel 136 into which a batch of oil is poured. Connected tothe wall of the vessel [36 above the level of oil therein is a steamejector 138 which creates a partial vacuum above the oil in the vessel136. At the bottom of the vessel 136 is a conduit 140 connected to asupply of steam and having openings therein such that steam will bubbleup through the oil. The flow rate and density of the steam fed into thesystem are measured by flowmeter 142 and density meter I44,respectively. The steam output is fed through a total hydrocarbonsanalyzer 146 to a scrubber, not shown, where the volatiles arerecovered. The analyzer 146 is of the type based upon the flameionization principle.

, It is known that the higher the .vacuum above the oil in the vessel136, the shorter is the time required to complete deodorizing of a batchof oil. The vaporization efficiency of the process is also a function ofthe surface area of the steam bubbles passing upwardly through the oiland the time during which they are in contact with the oil. Thetemperature of the oil is a further factor in the control of theprocess, since it determines the vapor'pressures of the components whichare i to be removed. The hydraulic head of the oil in the vessel alsoexerts an effect on the amount of vaporization efficiency. I

Oil losses occur by entrainment in the steam exhausted from thedeodorizer vessel and by distillation of the free fatty acids which canbe formed by hydrolysis. In the case of the free fatty acids, therecomes a point where the formation of them by hydrolysis equals the rateof distillation.-With regard to entrainment ,-the higher the steam flowrate. the higher the oil losses. Less steam is. however, required when ahigher vacuum can be obtained. Both oil losses and deodorizing time arereduced at higher vacuums. However, the capacity of the vacuumquantities S, and S, are determined and fed back to the generatingsystem to handle vapors is limited. The amount of vacuum will also varyfrom time-to-time dependent on the availability and pressure of thesteam supplied to the ejectors and to the cooling water temperaturesupplied to the barometric condensers in the scrubber. This is thus amajor constraint on the system.

The real check on completion of the deodorizing process is the rate ofchange of volatile content in the vapor. Reaching a low asymptotic valueis an indication that an equilibrium condition has been established andthat no further improvement can be made in the oil by additional time inthe vessel. The operation is advised of this effect via the totalhydrocarbons analyzer 146 such that the deodorizing process can beterminated and the batch removed.

It is also possible to estimate the total amount of volatiles of alltypes driven off between times t and l, for a constant stripping steamflow. The basic relationship between the total amount of steam, S,required to reduce the volatiles from concentration V to concentration Vis:

the vaporization efficiency and the total amount of oil. Thus, if thetotal amounts of stripping steam S, and S consumed between times I,, andt, and between times t, and 1 respectively, are known together with thecorresponding amounts of volatiles driven off, V, and V then:

i =k (VA/VA V1) and 2 in w. mm m Va] From the foregoing equations, theconstants k and V can, be solved by the computer. The amounts ofvolatiles V, and V; are determined and fed back to the computer by thetotal hydrocarbons analyzer 146 while the computer from the elements 142and 144. Knowing now the quantity V and the desired value of V,,, thetotal amount of steam reguired'may be calculated; and, knowing thestripping steam rate, the time required for the volatiles concentration.to -fall to the value V can be estimated. As will be appreciated, thecomputer can then automatically terminate the flow of steam at thedesired value or can produce an 'indication such that the operator canperform this function manually.

Although the invention has been shown in connection with certainspecific embodiments, it will be read- .ily apparent to those skilled inthe art that various changes in form and arrangement of'parts may bemade I to suit requirements without-departing from the spirit and: scopeof the invention.

clai m myinvention: :ij; fl. a system j'forhydrogenating unsaturatedliquid hydrocarbons, the combination of a vessel containing liquidunsaturated hydrocarbons-td'be hydrogenated and having a gas-filledspace above the level of the liquid hydrocarbons therein, means forbubbling hydrogen through the hydrocarbons within said vessel, means forpurging at least a portion of the gases above the liquid level ofhydrocarbons in said vessel, means for producing electrical signal meanswhich varies as a function of the amount of hydrogen fed into saidvessel. means for producing electrical signal means indicative of theamount of hydrogen purged from said vessel, computer means responsive toboth of said electrical signal means for computing the amount ofhydrogen absorbed by said liquid hydrocarbons, and control means coupledto said computer means for stopping the flow of hydrogen into saidvessel when the amount of hydrogen absorbed by the hydrocarbons hasreached a desired value.

2. The combination of claim 1 including means for producing anelectrical signal which varies as a function of the pressure of thegases above the level of the liquid hydrocarbons in said vessel, andmeans including said computer means for controlling the pressure of thehydrogen fed into said vessel as a function of the magnitude of saidsignal which varies as a function of pressure.

'3. The combination of claim 1 including cooling coil means within saidvessel, means for producing an electrical signal which varies as afunction of the temperature of the liquid hydrocarbons within saidvessel, and means including said computer means responsive to saidelectrical signal for controlling the amount of coolant passing throughsaid cooling coil means.

4. The combination of claim 1 including a flowmeter, a density meter anda thermal conductivity analyzer through which hydrogen purged from saidvessel is passed and wherein the amount of hydrogen purged from saidvessel is determined by electrical signals fed to said computer fromsaid flowmeter, the density meter and the thermal conductivity analyzer.

2. The combination of claim 1 including means for producing anelectrical signal which varies as a function of the pressure of thegases above the level of the liquid hydrocarbons in said vessel, andmeans including said computer means for controlling the pressure of thehydrogen fed into said vessel as a function of the magnitude of saidsignal which varies as a function of pressure.
 3. The combination ofclaim 1 including cooling coil means within said vessel, means forproducing an electrical signal which varies as a function of thetemperature of the liquid hydrocarbons within said vessel, and meansincluding said computer means responsive to said electrical signal forcontrolling the amount of coolant passing through said cooling coilmeans.
 4. The combination of claim 1 including a flowmeter, a densitymeter and a thermal conductivity analyzer through which hydrogen purgedfrom said vessel is passed and wherein the amount of hydrogen purgedfrom said vessel is determined by electrical signals fed to saidcomputer from said flowmeter, the density meter and the thermalconductivity analyzer.